Anisotropic heat shield construction



Dec. 21, 1965 J. F. LOPRETE ETAL ANISOTROPIC HEAT SHIELD CONSTRUCTIONFiled June 25, 1965 5 Sheets-Sheet 1 INVENTORS .JUEJEFH F. LE] ETE. RDCANBI EIEI WEQ L ATTEIRNEY Dec. 21, 1965 J. F. LOPRETE ETAL 3,224,193

ANISOTROPIC HEAT SHIELD CONSTRUCTION 3 Sheets-Sheet 2 Filed June 25,1963 ATTI'JRNEY Dec. 21, 1965 J. F. LOPRETE ETAL ANISOTROPIG HEAT SHIELDCONSTRUCTION Filed June 25, 1963 3 Sheets-Sheet 5 INVENTORS LJEIEIEFH F.LDF'RETE QYRTHLIR QEANEIIALEIEII ATTEIR NEY 3,224,193 Patented Dec. 21,1965 Fice 3,224,193 ANISOTROPIC HEAT SHIELD CONSTRUCTIQN Joseph F.Loprete, Wayne, and Arthur I). Cangialosi, Clifton, NJ, assignors toCurtiss-Wright Corporation, a corporation of Delaware Filed June 25,1963, Ser. No. 290,395 18 Claims. (Cl. (SO-35.6)

This invention relates to heat shield structures and is particularlydirected to a novel construction for heat shield structures utilizinganisotropic materials.

Although the invention described herein relates to exhaust nozzles ofjet engines or the like, it is not intended that the invention is solimited. Thus, the invention is also applicable as a heat shield foraircraft, missiles, space vehicles, atmosphere re-entry vehicles andother devices intended to travel through space or the atmosphere or anypart thereof which may be exposed to high temperatures for a limitedperiod of time.

It is known in the case of rockets and jet engines to use a specialmeans for cooling the exhaust nozzles, such as for example, a liquidcoolant. In planning for higher thrust devices the problem arises thatthe propellants used in such devices burn at higher temperatures whichmay be in excess of 6000 F. Accordingly, it follows that exhaust nozzlescapable of withstanding these higher temperatures must be provided. Itis a prime object of the present invention to provide a novel exhaustnozzle construction which is capable of withstanding relatively hightemperature conditions while avoiding the serious problem of erosion ofthe gas wall at the nozzle throat area.

The invention makes use of the relatively unique properties of a knownform of graphite called pyrolytic graphite. The pyrolytic graphitematerial is normally deposited on a substrate layer which usually is aconventional graphite. As the pyrolytic graphite is deposited, it formsa layer having marked anisotropic properties. Along the plane of depositor in other Words along a plane parallel to the deposited layer, thepyrolytic graphite is highly thermally conductive and has a relativelylow coefficient of thermal expansion in this direction while in adirection perpendicular to the plane of deposit the material is highlynon-conductive but with a relatively high coefficient of thermalexpansion in this direction. The heat conduction characteristics ofpyrolytic graphite are particularly significant at high temperaturesbecause of the high temperature properties of graphite. In addition theheat insulating property of pyrolytic graphite increases with increasein temperature. The present invention utilizes the above properties ofpyrolytic graphite in providing a novel exhaust nozzle construction witha nozzle heat sink with sutficient capacity to substantially eliminateerosion of the nozzle gas Wall and particularly in the nozzle throatregion wherein temperatures are relatively extreme.

The construction of the present invention generally comprises aplurality of circumferentially disposed wedges of pyrolytic graphitewhich extend axially in a direction parallel to the nozzle axis. Theorientation of each of the pyrolytic graphite wedges is such that withrespect to the nozzle axis thermal conduction will be relatively high inan axial and radial direction while in a circumferential direction theconstruction will be relatively highly thermally non-conductive. Withthis construction the heat will flow from the normally hotter regions ofthe gas wall of the nozzle to portions having relatively coolertemperatures thereby lowering the nozzle throat gas wall temperatures. Apyrolytic graphite layer or layers may be provided around the outersurface of the wedges with the planes of said layer being oriented so asto act as a heat insulator at the radially outward portions of saidwedges and thereby form a heat shield for the supporting outer structureof the nozzle. The invention will be pointed out in more detail in thefollowing detailed description. Reference may also be made to co-pendingapplication Serial No. 125,253 filed July 19, 1961, invented by GeorgeKraus, now Patent No. 3,156,091 issued on November 10, 1964, for adilferent configuration of a jet engine nozzle utilizing pyrolyticgraphite.

Accordingly, it is an object of the invention to provide a novel andimproved heat shield structure for aircraft subject to high temperatureoperation.

It is another object of the invention to provide a novel and improvedheat shield construction having anisotropic heat properties.

It is still another object of the invention to provide a novel andimproved heat shield construction for an aircraft exhaust nozzle.

It is a further object of the invention to provide a novel and improvedheat shield construction for an aircraft exhaust nozzle which preventsexcessive heat and erosion in the region of the nozzle throat.

It is an additional object of the invention to provide a heat shieldconstruction for an aircraft exhaust nozzle having anisotropicproperties and wherein novel means are provided in said construction forconduction of heat and relief of compression stresses.

Other objects and advantages of the invention will become apparent uponreading the following detailed description with the accompanying drawingwherein:

FIG. 1 is a sectional view of an exhaust nozzle embodying the inventionand taken along line 11 of FIG. 2;

FIG. 2 is a sectional view of the exhaust nozzle of FIG. 1 taken alongline Z2 of FIG. 1;

FIG. 3 is a perspective view of one of the anisotropic elements of thenozzle of FIG. 1;

FIGS. 4-7 are diagrammatic views of a portion of an exhaust nozzleshowing modifications for varying the heat conduction in the nozzlethroat region; and

FIGS. 4A-7A are sectional views of one of the anisotropic elements ofthe nozzle taken along lines A-A of each of said FIGS. 4-7,respectively.

In FIG. 1 there is illustrated a multi-layer exhaust nozz-le 10 whichmay for example, be provided for a rocket, said nozzle 10 having anouter housing or load carrying member 12 which is suitably connected tothe casing 14 of a rocket as by bolts 16 or other suitable means. A sealmeans 18, as for example an O ring may be provided between the casing 14and housing 12 for preventing any gas leakage between said members. Thenozzle 10 has an inner surface 20 with a convergent-divergent profile,the throat region of which is indicated at 22. As indicated in FIG. 1the exhaust gases flow from the rocket in the directions of the arrowsshown in FIG. 1 and are expanded out the rear end of the nozzle 10opposite from the end of said nozzle attached to the rocket casing 14.The inner layer of the nozzle 10 is formed from a pinrality of abuttingwedges of pyrolytic graphite in a manner which will be more clearlyexplained below. As shown in FIG. 1 the wedges indicated at 24 extendsubstantially the entire length of the rocket nozzle in the direction ofthe axis aa of said nozzle.

As stated, the wedges 24 are preferably formed from pyrolytic graphitewhich material has definite anisotropic characteristics. The pyrolyticgraphite is obtained in a furnace by vapor deposition from carbonbearing vapor. The wedges 24 are formed by depositing pyrolytic graphiteon a flat surface, the graphite being deposited on said surface to forma sufiicient thickness for obtaining the desired size wedges to be usedin said nozzle 10. It is known that the thickness to which pyrolyticgraphite can be deposited is limited and therefore the wedge size islikewise limited. The pyrolytic graphite wedges are then formed bycutting and machining such a deposited layer of pyrolytic graphite suchthat a median plane between the sides of the wedge is substantiallyparallel to the plane of deposit of the pyrolytic graphite. The nozzleinner surface or layer is built up from a plurality of such wedgesdisposed in a circle to form a substantially annular ring shaped nozzlelayer about the nozzle axis aa. If it is found that the pyrolyticgraphite can be deposited in greater thickness, then of course, thickerwedges and therefore a lesser number may be used.

The wedges 24 of the invention have their layer or deposited planedisposed so that said plane substantially includes the axis a-a of thenozzle and about which said wedges are circumferentially arranged toform a circle coaxial with said axis.

In other words, each wedge member 24 is made up of a layer plane ofpyrolytic graphite which extends along the length of said wedge and thenozzle is constructed so that each layer plane lies in a plane passingthrough the axis a-a of said nozzle 10.

As already stated, pyrolytic graphite has very pronounced anisotropicproperties in particular with respect to heat conduction and insulation.In directions parallel to the plane of deposit, the pyrolytic graphitehas excellent heat conduction properties while in a directionperpendicular to said plane the pyrolytic graphite is an excellent heatinsulator. With reference to FIG. 3 wherein there is shown one of theWedges 24 of the invention, from the discussion above, it will be seenthat, in directions longitudinally and radially relative to the nozzleaxis as well as in any other direction parallel to the surfaces ormedian plane of each of the wedges, there will be good heat conductionwhile in a direction substantially perpendicular to the median plane ofeach of said wedges 24 there will be little heat conduction. From theillustration of FIG. 3, it will be apparent that when a plurality ofwedges 24 are disposed in the manner shown in FIGS. 1 and 2 to form thenozzle interior, the nozzle will have high heat conduction in directionsaxial along the axis aa and radially from said axis. However, in acircumferential direction with respect to said axis aa, that is in adirection from one wedge to the adjacent wedge, the nozzle will havehigh heat insulating properties with little heat being conducted aroundthe nozzle in said circumferential direction. It will be apparenttherefore that as the hot combustion gases flowing through the nozzle 10from the rocket, the heat will be relatively rapidly conducted away fromthe inner surface of the nozzle throat region 22 and since the heattransfer from the exhaust gases to the nozzle is a maximum in the regionof the nozzle throat, there will be a flow of heat longitudinally andradially outwardly in each wedge 24 from the nozzle throat region. Asstated, the heat conduction will be radially away from the nozzle throat22 and axially along said nozzle so that the heat is conducted from thearea of said nozzle exposed to extreme temperatures to regions of saidnozzle which are relatively cool. Thus, it will be seen that heatsaturation in the nozzle throat area is delayed by allowing the heat toflow into portions of the nozzle which are relatively cool therebyforming a very efficient heat sink. As is well known in rocket nozzles,erosion of the nozzle throat area is a major problem which is caused bythe region of a nozzle throat area becoming heat saturated and rising toa temperature wherein this region may decompose. In the presentinvention erosion is completely eliminated since the heat is conductedaway from the nozzle throat area so that said nozzle throat area doesnot reach a temperature wherein decomposition may take place. Also, asexplained above, pyrolytic graphite has relative high rate of thermalexpansion in the direction of good heat insulation. In the presentinvention however, since good heat conduction is providid in axial andradial directions with relatively low thermal expansion in thesedirections, a problem in prior rocket nozzles of thermal expansion inthe axial direction is substantially eliminated. This eliminates theneed for providing bulky expansion joints to compensate for said thermalexpansion. However, as a safely factor a slight annular space 26 isprovided at the axial end of the nozzle adjacent the rocket engine toprovide for any axial expansion that might take place. The axialexpansion is relatively low in the present invention and has been foundto be in the neighborhood of 0.004 in./in. of length.

As also explained above, pyrolytic graphite has good heat insulationproperties in a direction perpendicular to the plane of deposit which inthe orientation of the wedges 24 illustrated in FIGS. 1 and 2 is acircumferential direction with respect to the nozzle axis 41-41. In thisdirection however, each of the wedges is subject to relatively highthermal expansion. In order to compensate for the thermal expansion inthe circumferential direction, each of the wedges is undercut along asubstantial portion of one of its faces as indicated at 28. A smallportion of each said undercut faces is not undercut so that when thewedges 24 are placed in position as illustrated in FIGS. 1 and 2, eachof said Wedges will abut against the adjacent wedge in the region of thegas wall to prevent gas leakage into the undercut region. The amount ofthe undercut is set to limit contact between the wedges due to thecircumferential thermal expansion of the pyrolytic graphite but alsoassures contact between the adjacent wedges at the gas wall. Theundercut minimizes the amount of restrained material thereby minimizingthe wrap thickness required to restrain the thermal expansion and makesthe required restraining loads uniform over the length of the wrapthereby eliminating the complication of a wrap of non-uniform thickness.Due to this construction, the nozzle suffers substantially nodeformation due to thermal expansion during operation and is capable ofcold restarts from operation to operation. It should be understood that,in lieu of the undercuts in each of the Wedges 24, spacers may beprovided between the wedges which would. permit expansion between thewedges while maintaining a gas tight seal at the inner surface of thenozzle.

An intermediate layer 20 of pyrolytic graphite which may take the formof a sleeve or a plurality of sleeves (three as illustrated) is placedin surrounding engagement with the wedges 24 with the plane of depositof said intermediate layer 29 being disposed to provide heat insulationin a radial direction with respect to the nozzle axis a-a. As shown inFIG. 2 each of the sleeves of the intermediate layer 29 is preferablyformed from a plurality of sleeve segments, there being four illustratedfor each sleeve, in order to provide for slight circumferentialexpansion of the nozzle. The intermediate layer 29 forms a heat shieldaround the outer diameter of the wedges 24, as illustrated, to protectthe housing or load carrying layer 12 from the heat conducted radiallyoutwardly from hot exhaust gases passing through the; nozzle. Radiallyoutwardly of the sleeves of the inter-- mediate layer 29 and in tightsurrounding engagement. therewith is a wrapping which may comprise atight fiting sleeve, bands or filaments made of various materialssuch assteel, plastic, glass fiber or other metals. The wrap or outer layer 30is fit in tight engagement with the intermediate layer 29 and serves tomaintain gas tight contact between the wedges 24 and to minimize thethroat area change due to thermal expansion. This is achieved bypre-loading and restraining the heat sink, thereby inducing high butallowable compressive stresses between adjacent wedges. Supported ateach axial end of the nozzle are a ring member 32 and a ring member 34,respectively, said rings 32 and 34 being formed from pyrolytic graphiteand having their plane of deposit oriented so that said rings arenon-conductive or highly heat insulating in the axial direction withrespect to the nozzle axis a-a. The function of the rings 32 and 34 issimilar to that of the intermediate layer 28, that is to function as aheat shield for the load carrying member or housing 12 at its axial endsas well as for the adjacent end of the rocket casing 14 so that thesemembers are protected from the heat of the hot exhaust gases.

It will be apparent from the above detailed description that a novelnozzle construction has been provided for high temperature operation.Due to the radial and axial heat conducting characteristics of thenozzle construction, the heat will be relatively rapidly carried awayfrom the nozzle throat region wherein temperatures are most extreme andthus prevent the possibility of erosion of the gas wall at said nozzlethroat region. The heat is conducted away from the above mentionedhighly-heated region to other regions of the nozzle that are relativelycool, thus preventing heat saturation of the heat sink in the highlyheated regions. Further, the construction substantially eliminates axialthermal expansion of the heat sink so that cold restarts are permittedwithout the use of bulky expansion joints. It has also been found thatthe novel construction of the invention increases the critical depth ofthe heat sink, or outside radius, to which heat reduction can beobtained with increases in depth in the nozzle construction. It is knownthat the critical depth decreases with increasing convective heattransfer coefficient which is highest in the region of the nozzlethroat. The invention keeps the nozzle throat relatively cool byconducting heat into portions of the heat sink where lower temperaturesexist.

Erosion of the gas wall immediately forward and aft of the nozzle throatregion has relatively little effect on the nozzle performance ascompared to erosion in the throat region itself. It has been found thatfurther decreases in the nozzle throat temperatures can be had in thenozzle construction of the invention at the expense of increasing thetemperature forward and aft of the throat by modifying the heat sinkformed by the wedge construction. In FIGS. 47 there are showndiagrammatic views of a portion of a wedge construction nozzle with theheat conduction paths being indicated by the arrows therein for thevarious modifications with FIG. 4 illustrating the heat conduction for anozzle having wedges without modification. For purposes of illustration,the arrows shown in said figures only purport to show the heatconduction in a substantially radial direction with respect to thenozzle axis. It will be seen in FIG. 4 that the radial heat conductionin the nozzle 10a illustrated therein flows in a direction substantiallyperpendicular to the inner surface a toward the outer surface of thenozzle 10a and tends to flow toward the center portion of the nozzlethroat region. As seen in FIG. 4A, wherein one of the wedges 24a isshown, the heat may be conducted radially through the wedge 24a withoutany substantial interruption. Therefore, it will be apparent that theheat conducted through the wedges 24a has a tendency to concentrate at aregion above the nozzle throat area thus limiting the heat that can beconducted from the nozzle throat. The modifications in FIGS. 57 and 5A-7A serve to control the flow of heat from the region of the nozzleforward and aft of the throat region into the heat sink region of thenozzle throat area and increase the heat capacity characteristics insaid nozzle throat area.

In FIGS. 5 and 5A there is shown a nozzle 1% with the wedges 24b of saidnozzle 10b having radiation gaps 36 and 38 formed therein to isolate theheat sink in the nozzle throat region. The radiation gaps are formed bycutting a portion through each wedge 2412 as shown in 6 FIG. 5A whichupon assembly of the wedges into the nozzle forms the radiation gaps 36and 38 illustrated in FIG. 5. Due to the orientation of the radiationgaps 36 and 38 a substantially trapezoidal-shaped heat sink is formed inthe nozzle throat region. As seen from the radially heat conductingarrows of FIG. 5, the heat conducted at the gas wall forward and aft ofthe nozzle throat region is prevented from flowing into the nozzlethroat heat sink region which, therefore, limits the amount of heatconducted into this region. As stated above, the heat conducted into theregion forward and aft of the throat region is not critical to theoperation of the nozzle and, therefore, heat saturation at these pointsin itself is not detrimental. However, due to the fact that less heat isconducted into the nozzle throat heat sink region from the region foreand aft of said nozzle throat, this permits a greater amount of heat tobe conducted from the nozzle throat region itself into its heat sinkbefore heat saturation will occur thereby permitting the nozzle throatto operate a substantially longer period before the decompositiontemperature will be reached.

In FIGS. 6 and 6A there is shown a second modification wherein there isprovided in the nozzle 10c two cone members 40 and 42 formed ofpyrolytic graphite and having their plane of deposit disposed toinsulate against heat conduction in a substantially axial direction. Theheat flowing from the regions fore and aft of the nozzle throat in thisembodiment cannot flow into the nozzle heat sink region adjacent thethroat area due to the insulating properties of the cones 40 and 42although heat will be conducted in a substantially radial directionalong said cones 40 and 42. This embodiment functions in a similarmanner as that of FIGS. 5 and 5A in that the heat sink in the nozzlethroat area is not saturated with heat from the regions fore and aft ofsaid nozzle throat area, thus increasing the capacity of the heat sinkin this region for cooling the nozzle throat gas wall.

FIGS. 7 and 7A show a third embodiment of the invention wherein aportion along each longitudinal face of the wedges 24a. is cutout asillustrated in FIG. 7A to form a heat choke. As illustrated in FIG. 7,when the wedges are placed together in the nozzle a heat choke is formedat the regions forward and aft of the nozzle throat area with said heatchoke extending substantially parallel to the gas wall in these regions.Each heat choke 44 and 46 serves to bring about an abrupt reduction inthe heat flow area from the region forward and aft of the nozzle throatarea to block the heat flow into the interior of the heat sink forwardand aft of the throat region. The function of this embodiment,therefore, is similar to that of the embodiments described above.

The invention has been illustrated and described in connection with arocket engine exhaust nozzle. As previously stated, however, theinvention has other applications particularly where a part is exposed tohigh temperatures for a limited period of time. For example, it may beused as a heat shield to protect the load carrying structure of otheraircraft parts from the high tem peratures which exist at the externalsurface of those parts exposed to supersonic flow of the surroundingatmosphere thereover. The construction of the invention is applicablenot only for high temperature usage on the inner surface of aircraftparts, but may be used for high temperature operation of external partsof aircraft.

While the invention has been described in detail in its presentpreferred embodiment it will be obvious to those skilled in the art,after understanding the invention, that various changes andmodifications may be made therein without departing from the spirit andscope thereof. For example, in the region forward and aft of the nozzlethroat area other materials may be substituted for the pyrolyticgraphite since the temperature conditions in these areas are not ascritical as in the nozzle throat area. Also, the members maybe shapedwith arcuate sides instead of flat sides, as illustrated or with theplane of deposit other than substantially parallel to the median planeof each wedge member. It is intended in the appended claims to cover allsuch modifications.

We claim:

1. An exhaust gas nozzle construction for jet engines or the likecomprising a nozzle having a substantially annular housing; a layercoaxially supported in said housing and having an inner surface whichsubstantially conforms to at least a portion of the inner nozzlesurface, said layer being composed of an anistropic material oriented sothat said material is relatively highly thermally conductive in planessubstantially including the nozzle axis and relatively highly thermallynon-conductive in a circumferential direction about said axis.

2. An exhaust gas nozzle construction as recited in claim 1 wherein saidlayer comprises a plurality of substantially wedge-shaped memberscomposed of pyrolytic graphite, said wedge-shaped members being disposedadjacent each other in a circle about the nozzle axis with the sides ofeach wedge-shaped member tapering toward the nozzle axis and said layerhaving a substantially annular cross-section.

3. An exhaust gas nozzle construction as recited in claim 2 wherein saidwedge-shaped members extend axially along the nozzle axis with at leasta portion of each side of each said Wedge-shaped members being placed intight operative engagement with an adjacent wedge-shaped member.

4. An exhaust gas nozzle construction as recited in claim 3 wherein eachof said wedge-shaped members has a portion of at least one of its sidescut back for providing a circumferential spacing between adjacentwedge-shaped members such that said spacing permits thermal expansionbetween adjacent wedge-shaped members in a circumferential directionrelative to said nozzle axis.

5. An exhaust gas nozzle construction as recited in claim 4 wherein eachwedge-shaped member has an undercut portion over a substantial portionof one face thereof and at the radially inner portion thereof having aland on said one face for abutting an adjacent wedgeshaped member .toprovide a substantially gas tight structure for the radially innersurface of said layer.

6. An exhaust gas nozzle construction as recited in claim 3 wherein eachwedge-shaped member has a plurality of gaps formed therein extendingbetween the sides thereof; and said gaps of each wedge-shaped memberbeing aligned with the gaps of adjacent wedgeshaped members to form aplurality of radiation gaps in said layer, said radiation gaps beinginclined from the nozzle throat with respect to the inner surface ofsaid nozzle and extending from a region adjacent the nozzle throatsubstantially into the regions of said layer forward and aft of thenozzle throat for limiting the conduction of heat into the region ofsaid layer adjacent the nozzle throat from the regions of said layerforward and aft of the nozzle throat.

7. An exhaust gas nozzle construction as recited in claim 3 wherein saidwedge-shaped members are of multi-par-t construction; said layer furthercomprising at least two facing cone-shaped members composed of pyrolyticgraphite spaced between adjacent parts of each of said wedge-shapedmembers with said cone-shaped members separating the nozzle throatregion of said layer from the regions of said layer forward and aft ofsaid nozzle throat region; and said cone-shaped members being orientedin said layer for relatively high heat insulation in a directionsubstantially parallel to the direction of gas flow through said nozzlesuch that heat is substantially prevented from flowing into the regionof said layer adjacent the nozzle throat from the region of said layerforward and aft of said nozzle throat.

8. An exhaust gas nozzle construction as recited in claim 3 wherein eachwedge-shaped member has a channel cut in each said side thereof and saidchannels of each wedge member being aligned with the channels ofadjacent Wedge-shaped members to form at least two heat chokes in saidlayer, said heat chokes extending substantially parallel to the innersurface of said nozzle from the region adjacent the nozzle throat intothe regions of said layer forward and aft of the nozzle throat to theregion adjacent the axial ends of said layer for limiting conduction ofheat into the region of said layer adjacent the nozzle throat from theregions of said layer forward and aft of the nozzle throat.

9. An exhaust gas nozzle construction as recited in claim 1 comprising;an intermediate layer of anistropic material in surrounding engagementwith said firstmentioned layer; and said intermediate layer having anorientation such that it is relatively highly thermally non-conductivein a radial direction with respect to the axis of said nozzle forforming a heat shield around the radially outer surface of saidfirst-mentioned layer.

10. An exhaust gas nozzle construction as recited in claim 9 whereinsaid intermediate layer includes an annular sleeve member comprising aplurality of circumferentially-spaced sleeve segments for permittingcircumferential expansion of said segments.

11. An exhaust gas nozzle construction as recited in claim 9 whereinsaid nozzle has a convergent-divergent flow path for the exhaust gasesflowing therethrough; and the radial depth of said first-mentioned layerbeing substantially greater than the radial depth of said intermediatelayer at least in the region of said nozzle throat.

12. An exhaust gas nozzle construction as recited in claim 9 furthercomprising an outer layer surrounding said intermediate layer with saidouter layer in tight fitting engagement with said intermediate layer forsupporting said first-mentioned and intermediate layers in said nozzlehousing and said outer layer extending substantially the entire lengthof the inner surface of said nozzle housing.

13. An exhaust gas nozzle construction as recited in claim 1 furthercomprising a ring member composed of anisotropic material supported ateach axial end of said nozzle in engagement with said layer with saidanisotropic material of said ring members being oriented for relativelyhigh thermal non-conduction in a direction substantially parallel to theaxis of said nozzle for providing a heat shield at said axial ends ofsaid layer.

14. An exhaust gas nozzle construction as recited. in claim 13 whereinsaid ring member at the axial gas receiving end of said nozzle is spacedfrom the axial end of said nozzle housing for permitting slight axialthermal expansion of said nozzle construction.

15. An aircraft part or the like having a surface exposed to hightemperature gas flow thereover, said part having structural loadcarrying means; an intermediate layer of heat insulating materialdisposed over said load carrying means; a layer of material disposedover said intermediate layer and having its surface remote from saidintermediate layer exposed to said high temperature gas flow, and saidlayer being composed of an anisotropic material with said material beingoriented so that at least at its surface remote from said intermediatelayer has its relatively high thermal conduction in a first directionsubstantially parallel to the direction of gas flow and a seconddirection substantially perpendicular to the direction of gas flow andhaving relatively high thermal non-conduction in a third directionperpendicular to said first and second directions.

16. An aircraft part as recited in claim 15 wherein said anisotropicmaterial is pyrolytic graphite.

17. An aircraft part as recited in claim 16 wherein said intermediatelayer is composed of pyrolytic graphite 9 it} With said pyrolyticgraphite being oriented so that it is References Cited by the Examinerrelatively highly thermally non-conductiye in a direc- UNITED STATESPATENTS tion substantlally perpendicular to the direction of gas flowfor providing good heat insulation between said 3,137,132 6/1964 Turkat60-355 second-mentioned layer and said load carrying means. 5

18. An aircraft part as recited in claim 17 wherein the thickness ofsaid second-mentioned layer is substantially greater than the thicknessof said intermediate MARK NEWMAN Prlmmy Exammer' layer. SAMUEL LEVINE,Examiner.

1. AN EXHAUST GAS NOZZLE CONSTRUCTION FOR JET ENGINES OR THE LIKECOMPRISING A NOZZLE HAVING A SUBSTANTIALLY ANNULAR HOUSING; A LAYERCOAXIALLY SUPPORTED IN SAID HOUSING AND HAVING AN INNER SURFACE WHICHSUBSTANTIALLY CONFORMS TO AT LEAST A PORTION OF THE INNER NOZZLESURFACE, SAID LAYER BEING COMPOSED OF AN ANISTROPIC MA-